util/concurrent/CopyOnWriteArraySet.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;
import java.util.*;

/**
 * A {@link java.util.Set} that uses {@link
 * java.util.concurrent.CopyOnWriteArrayList} for all of its
 * operations.  Thus, it shares the same basic properties:
 * <ul>
 *  <li>It is best suited for applications in which set sizes generally
 *       stay small, read-only operations
 *       vastly outnumber mutative operations, and you need
 *       to prevent interference among threads during traversal.
 *  <li>Mutative operations(add, set, remove, etc) are expensive
 *      since they usually entail copying the entire underlying array.
 *  <li>Loops involving repeated element-by-element mutative operations
 *      are so expensive that they should generally be avoided.
 *  <li>Iterators do not support the mutative remove operation
 *  <li>Traversal via iterators is very fast and cannot ever encounter
 *      interference from other threads. Iterators rely on
 *      unchanging snapshots of the array at the time the iterators were
 *     constructed.
 * </ul>
 * <p>
 * <b>Sample Usage.</b> Probably the main application
 * of copy-on-write sets are classes that maintain
 * sets of Handler objects
 * that must be multicasted to upon an update command. This
 * is a classic case where you do not want to be holding a
 * lock while sending a message, and where traversals normally
 * vastly overwhelm additions.
 * <pre>
 * class Handler { void handle(); ... }
 *
 * class X {
 *    private final CopyOnWriteArraySet handlers = new CopyOnWriteArraySet();
 *    public void addHandler(Handler h) { handlers.add(h); }
 *
 *    private long internalState;
 *    private synchronized void changeState() { internalState = ...; }
 *
 *    public void update() {
 *       changeState();
 *       Iterator it = handlers.iterator();
 *       while (it.hasNext())
 *          ((Handler)(it.next()).handle();
 *    }
 * }
 * </pre>
 * @see CopyOnWriteArrayList
 * @since 1.5
 * @author Doug Lea
 */
public class CopyOnWriteArraySet<E> extends AbstractSet<E>
        implements Cloneable, java.io.Serializable {

    private final CopyOnWriteArrayList<E> al;

    /**
     * Constructs an empty set.
     */
    public CopyOnWriteArraySet() {
        al = new CopyOnWriteArrayList<E>();
    }

    /**
     * Constructs a set containing all of the elements of the specified
     * Collection.
     * @param c the collection
     */
    public <T extends E> CopyOnWriteArraySet(Collection<T> c) {
        al = new CopyOnWriteArrayList<E>();
        al.addAllAbsent(c);
    }


    public int      size()                    { return al.size(); }
    public boolean  isEmpty()                 { return al.isEmpty(); }
    public boolean  contains(Object o)        { return al.contains(o); }
    public Object[] toArray()                 { return al.toArray(); }
    public <T> T[]  toArray(T[] a)            { return al.toArray(a); }
    public void     clear()                   {        al.clear(); }
    public Iterator<E>  iterator()            { return al.iterator(); }
    public boolean  remove(Object o)          { return al.remove(o); }
    public boolean  add(E o)                  { return al.addIfAbsent(o); }
    public boolean  containsAll(Collection<?> c)      { return al.containsAll(c); }
    public boolean  addAll(Collection<? extends E> c) { return al.addAllAbsent(c) > 0; }
    public boolean  removeAll(Collection<?> c)        { return al.removeAll(c); }
    public boolean  retainAll(Collection<?> c)        { return al.retainAll(c); }

}
Revision:	1.7
Committed:	Mon Aug 25 01:55:54 2003 UTC (20 years, 9 months ago) by dholmes
Branch:	MAIN
Changes since 1.6:	+5 -5 lines
Log Message:	Removed leading spaces on <li> elements
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7	tim	1.1	package java.util.concurrent;
8			import java.util.*;
9
10			/**
11	dl	1.3	* A {@link java.util.Set} that uses {@link
12			* java.util.concurrent.CopyOnWriteArrayList} for all of its
13			* operations. Thus, it shares the same basic properties:
14	tim	1.1	* <ul>
15	dholmes	1.7	* <li>It is best suited for applications in which set sizes generally
16	tim	1.1	* stay small, read-only operations
17			* vastly outnumber mutative operations, and you need
18			* to prevent interference among threads during traversal.
19	dholmes	1.7	* <li>Mutative operations(add, set, remove, etc) are expensive
20	tim	1.1	* since they usually entail copying the entire underlying array.
21	dholmes	1.7	* <li>Loops involving repeated element-by-element mutative operations
22	tim	1.1	* are so expensive that they should generally be avoided.
23	dholmes	1.7	* <li>Iterators do not support the mutative remove operation
24			* <li>Traversal via iterators is very fast and cannot ever encounter
25	tim	1.1	* interference from other threads. Iterators rely on
26			* unchanging snapshots of the array at the time the iterators were
27			* constructed.
28			* </ul>
29			* <p>
30			* <b>Sample Usage.</b> Probably the main application
31			* of copy-on-write sets are classes that maintain
32			* sets of Handler objects
33			* that must be multicasted to upon an update command. This
34	tim	1.5	* is a classic case where you do not want to be holding a
35	tim	1.1	* lock while sending a message, and where traversals normally
36			* vastly overwhelm additions.
37			* <pre>
38	tim	1.6	* class Handler { void handle(); ... }
39	tim	1.1	*
40			* class X {
41			* private final CopyOnWriteArraySet handlers = new CopyOnWriteArraySet();
42			* public void addHandler(Handler h) { handlers.add(h); }
43			*
44			* private long internalState;
45			* private synchronized void changeState() { internalState = ...; }
46			*
47			* public void update() {
48			* changeState();
49			* Iterator it = handlers.iterator();
50			* while (it.hasNext())
51			* ((Handler)(it.next()).handle();
52			* }
53			* }
54	tim	1.6	* </pre>
55	tim	1.1	* @see CopyOnWriteArrayList
56	dl	1.4	* @since 1.5
57			* @author Doug Lea
58			*/
59	tim	1.1	public class CopyOnWriteArraySet<E> extends AbstractSet<E>
60			implements Cloneable, java.io.Serializable {
61
62			private final CopyOnWriteArrayList<E> al;
63
64			/**
65	tim	1.6	* Constructs an empty set.
66	tim	1.1	*/
67			public CopyOnWriteArraySet() {
68			al = new CopyOnWriteArrayList<E>();
69			}
70
71			/**
72			* Constructs a set containing all of the elements of the specified
73			* Collection.
74	dl	1.4	* @param c the collection
75	tim	1.1	*/
76			public <T extends E> CopyOnWriteArraySet(Collection<T> c) {
77			al = new CopyOnWriteArrayList<E>();
78			al.addAllAbsent(c);
79			}
80
81
82			public int size() { return al.size(); }
83			public boolean isEmpty() { return al.isEmpty(); }
84			public boolean contains(Object o) { return al.contains(o); }
85			public Object[] toArray() { return al.toArray(); }
86			public <T> T[] toArray(T[] a) { return al.toArray(a); }
87			public void clear() { al.clear(); }
88			public Iterator<E> iterator() { return al.iterator(); }
89			public boolean remove(Object o) { return al.remove(o); }
90			public boolean add(E o) { return al.addIfAbsent(o); }
91	tim	1.5	public boolean containsAll(Collection<?> c) { return al.containsAll(c); }
92			public boolean addAll(Collection<? extends E> c) { return al.addAllAbsent(c) > 0; }
93			public boolean removeAll(Collection<?> c) { return al.removeAll(c); }
94			public boolean retainAll(Collection<?> c) { return al.retainAll(c); }
95	tim	1.1
96			}